This invention relates to a fuel injection pump for internal combustion engines, and more particularly to a centrifugal injection timing control device for use in in-line type fuel injection pumps.
Conventional centrifugal injection timing control devices for use with in-line type fuel injection pumps for diesel engines include an eccentric type, as disclosed e.g. in Japanese Provisional Patent Publication (Kokai) No. 54-3617, which comprises a driven rotary member adapted to be coupled to a camshaft of the fuel injection pump, a driving rotary member adapted to be coupled to an output shaft of the engine, a housing rigidly fitted on the driven rotary member for rotation in unison therewith, centrifugal weight means accommodated within the housing and displaceable diametrically thereof in response to rotation of the driven rotary member, and double eccentric cam means interposed between the driving rotary member and the centrifugal weight means and engaging with both of them.
According to the above centrifugal injection timing control device, the centrifugal weight means includes a pair of centrifugal weight members arranged diametrically oppositely with respect to the driven rotary member. Each of the centrifugal weight members is disposed to define a radially inner chamber in cooperation with the driven rotary member and a radially outer chamber in cooperation with the housing. The housing has it interior filled with oil for lubricating various parts of the injection timing control device. When the centrifugal weight members are in their non-lifted or retracted position, they abut against each other by means of spring means incorporated therein, to define therebetween an annular enclosed space, i.e. the above radially inner chamber, in cooperation with the driven rotary member, thus preventing the oil in the radially inner chamber from flowing into the radially outer chamber, as well as preventing the oil in the radially outer chamber from flowing into the radially inner chamber. As a consequence, a hysteresis characteristic exists in the action of the centrifugal weight members between the lifting stroke and the retracting or returning stroke, which makes it difficult to achieve a proper injection timing characteristic.
Further, there is a problem that the injection timing device of this type cannot have the same injection timing characteristic when it is in actual use with an engine as that obtained by adjustment in the factory.